乳房撮影専用 X 線装置の基本特性 : 半価層の測定

Abstract

X-ray beam quality is one of the most important factors in image contrast of mammograms. Using an X-ray mammography unit, model GE/CGR Senographe 600 T Senix H. F., we investigated the beam quality in terms of : a) the HVL (half-value layer) within the operating range of tube voltage used in mammography, b) a breast compression plate varies the HVL or not, c) variation of HVLs in an X-ray field, and d) problems caused by an unique geometry of the mammography unit concerning HVL measurements. The following results were obtained. a) The HVLs at 26-30kV with the compression plate increases about more than 12% in comparison with that when it is removed. b) The HVL at 26kV with the compression plate is nearly equal to that at 30kV without it. c) The HVL varies in any position of the X-ray field by the heel effect of the X-ray tube. The HVL is smallest at the center posittion near the tube cathode side (i. e., at the center position near chest wall side), at the both ends near the tube cathode side and the center position between the cathode and anode sides on the center line of the image receptor support device, the HVL is about 2% greater than that at the center position near the tube cathode side. Also, the HVL near the anode side is about 10% greater. Therefore, we propose that the measurement of the HVL should be carried out at the center position near the tube cathode side in the X-ray field based on clinical use.